A compressor control system is known from Japanese Patent Laid-Open No. 60-60286/1985. The control system disclosed in this reference provides a motor output torque in synchronism with the change of a load torque applied in one revolution of a motor rotor for driving a compression element of the compressor. In other words, the control system always detects the load torque during one revolution of the rotor and changes the motor output in such a manner as to correspond to this load torque.
Generally, as a rotating position detector of a compressor motor, a detector which detects the rotating position of the rotor by coupling directly a gear or an encoder to a spindle of the motor and disposing a sensor for detecting pulses at the time of revolution, is known as described in Japanese Patent Laid-Open No. 63-23585/1988.
In accordance with the control system of the compressor having the construction described above, the rotating position of the compressor must always be detected, and there remain problems in that a large number of position detectors are necessary, in that a high level of accuracy is required for this position detection, in that the outputs of the motor must be successively calculated and outputted sequentially, with the result being the control circuit becomes complicated.
In the rotating position detector of the motor having the construction described above, the sensor must be disposed directly inside the compressor and for this reason, the Freon resistance, temperature resistance requirements and pressure resistance of the sensor must be fulfilled and the service life of the sensor cannot be secured sufficiently. Though a sensor having an improved Freon resistance has been developed, a sufficiently long service life cannot yet be secured.